I am not a dancer so I've never written down choreography notes. Although there are some SMs on SMNet who do have dancing knowledge and skills and have been known to write it down, simply because they can.
Usually, in my experience, there has been a dance captain appointed within the cast to keep the cast on track in the event that the choreographer isn't there (such as performances). What I would recommend is to pay attention to the dancing, for spacing, set issues, lighting notes, costume notes, etc. Also, it would be beneficial to still write down groups (if dancing is done in groups) and exits, entrances and where the actors end up at the beginning and end of the dance, that way blocking can be picked up from those points.
It's certainly not a requirement, to my knowledge, but necessary to pay attention if you can.